SNAS669E September 2015 – April 2018 LMK03318
PRODUCTION DATA.
If used appropriately, dithering may be used to reduce sub-fractional spurs, but if used inappropriately, it can actually create spurs and increase phase noise. Table 5 provides guidelines for the use of dithering based on the fractional denominator, after the fraction is reduced to lowest terms.
FRACTION | RECOMMENDATION | COMMENTS |
---|---|---|
Fractional Numerator = 0 | Disable Dithering | This is often the worst case for spurs, and can actually be turned into the best case by disabling dithering. Performance is then similar to integer mode. |
Equivalent Denominator < 20 | Disable Dithering | These fractions are not well randomized and dithering will likely create phase noise and spurs. |
Equivalent denominator is not divisible by 2 or 3 | Disable Dithering | There will be no sub-fractional spurs, so dithering is likely not to be very effective. |
Equivalent denominator > 200 and is divisible by 2 or 3 | Consider Dithering | Dithering may help reduce the sub-fractional spurs, but understand it may degrade the PLL phase noise. |